What's the issue with this 9-png , showing black borders?

I have been struggling for a week to run this nine patch image by adding patches to it with all case but it doesn't work , I can't figure out why ? Any suggestions are highly appreciated.

It shouldn't show black lines when I am using it.

This is the layout code where I use this image ,

                    <Button
                    android:id="@+id/answerA"
                    android:layout_width="fill_parent"
                    android:layout_height="match_parent"
                    android:layout_marginRight="2dp"
                    android:layout_weight="1"
                    android:background="@drawable/d_grey"
                    android:gravity="center"
                    android:onClick="AnswerCheck" />

--Edit--

As suggested in an answer I opened this image in ninepatch tool and below is the screenshot for the same,

Possible solutions:

• Have you created 9-patch images properly? check out this site and create 9patch image.
• Do not remove .9 extension from image like sample.9.png
• Do not resize image after creating 9 patch image.
• Refresh-Clean-build project to apply changes you made in resource folders